In the manufacture of a conventional heat exchanger, heat exchanger tubes are inserted through respective aligned holes in a plurality of spaced-apart plate fins. Initially, the heat exchanger tubes are rather loosely received in the holes of the plate fins. It is necessary to expand the heat exchanger tubes in the holes of the plate fins so that the heat exchanger tubes are in a close-fitting, interference contact with the plate fins.
A conventional system for constructing heat exchangers using fluidic expansion by employing a fluid expansion is disclosed in U.S. Pat. No. 5,765,284 to Ali et al. As shown in FIG. 1, a compressor 2 of a tube expansion system 3 compresses an expansion fluid, specifically, a compressible fluid, from an expansion fluid reservoir 4 through a high-pressure safety valve 6 to the heat exchanger 8 via pipes 10a and 10b. The expansion fluid under high-pressure enters a tubing circuit 12 of the heat exchanger 8 through a connector 14 which is sealed to an inlet of the tubing circuit 12. The tubing circuit 12 is a serpentine structure of connected heat exchanger tubes 16. The connector 14 is a high-pressure connector capable of remaining sealed while delivering the expansion fluid at several thousand pounds per square inch. Upon introduction of the high-pressure fluid into the tubing circuit 12, the heat exchanger tubes 16 of the serpentine structure 16 expand radially outwardly to form secure contact with plate fins 18 and tube sheets 20. A plug 22 seals an outlet of the tubing circuit 12.
As shown in FIG. 1, controls 24 govern the amount of pressure the compressor 2 supplies to the tubing circuit 12. The controls 24 also terminate compression of the compressor 2 when sufficient expansion of the heat exchanger tubes 16 has been achieved by shutting off a power supply 26 supplying power to the compressor 2 through the controls 24. The controls 24 are used in conjunction with a displacement sensor 28. The displacement sensor 28 physically measures the increase in tubing diameter of a portion of one heat exchanger tube 16 of the tubing circuit 12. The displacement sensor 28 provides feedback of the expansion progress of the heat exchanger tubes 16 to the controls 24. In this manner, the controls 24 are set to stop the expansion of the heat exchanger tubes 16 once the circuit reaches a certain diameter. Alternatively, the controls 24 can vary the pressure of the expansion fluid during the expansion process. The controls 24 are essentially a microprocessor programmed in such a manner as to perform the above-stated objectives.
Another conventional tube expansion system for constructing heat exchangers uses an incompressible fluid such as water as opposed to U.S. Pat. No. 5,765,284 that uses a compressible fluid. However, other than one system using an incompressible fluid while the other uses a compressible fluid, the conventional systems for expanding heat exchanger tubes to construct heat exchangers using a fluid are generally similar in structure and function.